In the mass production of large machines, for example automobiles or trucks, it is standard to move a succession of large workpieces such as chassis slowly in steps through a succession of work stations at each of which some operation, such as mounting a part or welding a seam, is carried out. For most operations the workpieces must be stationary, so their advance is usually stepped, that is with periodic full halts in motion.
The machinery that acts on the workpieces is frequently mainly automatic so that the jobs are frequently done in the stations at a rate much faster than the conveyor stepping cadence. As a result some machines, particularly robot welders, are frequently idle much of the time, that is they weld everything in reach in their work station on the workpiece in much less time than the period of the conveyor.
The longitudinal spacing, that is in the direction of travel, must be at least equal to the workpiece length. In addition the delivery of parts to a robot installing them is complicated by distance problems, and the large mass of the succession of workpieces also puts an upper limit to travel speed of the workpieces.
In order to prevent a valuable industrial robot from standing idle once its assigned chore is complete, it is therefore standard practice as described in German patent document No. 2,350,603 filed Sept. 10, 1973 by J. Kraus to provide the robot with a tool turret carrying a multiplicity of different tools. Thus while the workpiece is stopped next to the robot it can sequentially carry out a succession of tasks, for instance boring and then tapping holes.
Even with such an arrangement, however, the robot is idle during the time when the workpieces are moving. Due to their high mass, as mentioned above, displacement speed is very slow so that it is not uncommon for a valuable robot to be actually working only half the time.
In addition all of the known industrial-robot production systems and methods are based on the standard straight-line production path with which production space can be increased by doubling back the line to form a plurality of parallel and adjacent production lines. In no manner is it possible to adapt these known systems to any arrangement giving more flexibility in layout of the production line, for instance having crossing line sections.